#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int main() {
    int k;
    int sum = 0, day = 0;
    scanf("%d", &k);
    for (int i = 1; i <= k; i++)
    {
        for (int j = 1; j <= i; j++)
        {
            sum += i;
            day++;
            if (day == k)
            {
                printf("%d", sum);
                break;
            }
        }
    }
    return 0;
}